Analysis and treatment of printing failure of the

Analysis and treatment of printing faults of web offset press

with the continuous improvement of people's material and cultural living standards, people's requirements for the printing quality of newspapers and commercial prints are also improving. The use of web offset printing machine will undoubtedly bring new opportunities and challenges to printing manufacturers, and it is particularly important to find and deal with printing faults in time

next, the author will briefly analyze the causes of the failure of the web offset press in the printing process and put forward the corresponding treatment methods, hoping to be helpful to readers

I. poor inking (looking at the version)

1 The inking part is not inked or slightly blurred

reason: the inking part of the printing plate is worn; The acidity of the fountain solution is too strong to emulsify the ink; Excessive pressure of the inking roller causes deinking of the inking roller

treatment method: replace the printing plate; Adjust the pH value of the fountain solution; Spray reducing agent on the inking roller or stop the machine to clean the inking roller, and readjust the pressure between the inking roller and the plate cylinder

2 can reduce the fire risk The inked part is not inked at all or shallow printing occurs repeatedly at the same part of each page

reason: the blanket is sunken

treatment method: apply reductant on the blanket or replace the blanket

II. Ink spots appear when the whole printing plate surface is stained with ink or chromaticity

reason: the plate is stained with dry glue during initial operation or the plate is dry when restarting; During normal operation, part of the landing roller is not in contact with the printing plate, and the water volume is insufficient due to improper pressure between the brush roller and the bucket roller or serious wear of the brush roller

treatment method: instantly increase the speed of the water supply motor to increase the water volume, so as to quickly remove the glue. If it is invalid, check whether the brush roller is worn. If the wear is serious, replace the brush roller. If the wear is not serious, adjust the pressure of the brush roller, plate roller and bucket roller

III. when starting printing, the non inking part is stained with a lot of paper powder

reason: when starting printing, if the ink in the organ newspaper arrives in front of the page, and the water roller contacts the page for a long time, the page will be polluted; If you do not adjust the ink in advance, but start printing when the ink roller is dry, it is particularly easy to cause this phenomenon

treatment: stop the machine immediately and wipe the page. Then change the set time to start printing. Before restarting the machine, adjust the ink on the ink roller first. If you only increase the water volume without stopping the machine, you will not be able to quickly remove the paper powder, but will cause the water ink ratio to be out of balance and the scrap rate to rise

IV. bad words and dots are damaged by ink

reason: excessive ink; High ink viscosity; The inking roller pressure is too high; Printing plate or rubber cloth lining is too thick; The pH value of fountain solution is inappropriate; The printing plate is worn

treatment method: reduce the speed of the ink supply motor or change the gap between the ink bucket and the ink bucket roller to reduce the amount of ink; Reduce ink viscosity; Readjust the pressure of the ink roller and the plate cylinder; Reduce the thickness of printing plate or rubber cloth lining; Change the pH value of the fountain solution; Replace the printing plate

v. the color of the granular inking part is thin and weak

reason: the speed of the water supply motor is too high; Insufficient ink; The pressure of plate cylinder and rubber cylinder is insufficient; The rubber blanket is cracked or stained; The inking part of the printing plate is worn; There is too much paper powder on the web

treatment method: reduce the speed of water supply motor; Increase the gap between the ink bucket and the ink bucket roller to increase the ink volume; Increase the lining thickness of printing plate or blanket; Wipe the blanket or replace it; Repair or replace the printing plate; Eliminate the paper powder on the web

VI. paper fuzzing and circular white spots, white spots on the printing surface, and black spots on the non inking part

reason: there is dirt on the blanket and inking roller; Foreign matters mixed in the ink; The surface of rubber blanket is sticky; The servo motor control system is adopted due to the excessive viscosity of the ink, so that the stretching, tightening speed and displacement can be controlled more accurately, and the paper fuzzes; There is too much paper powder on the web

treatment method: wipe the blanket and inking roller; Replace the ink or add liquid to the ink to eliminate foreign matters in the ink; Replace the blanket; Reduce the viscosity of ink with reducing agent; Eliminate the paper powder on the web

VII. The non inking part of the dirty version (dirty) is stained with ink; Ink viscosity is too high or too much ink makes the non inking part produce ink affinity

reason: poor plate making process; There is dirt on the water roller; Jumping or slipping caused by improper pressure of inking roller; The rubber blanket is loose or damaged; The pH value of fountain solution is inappropriate or the water quality is too hard; The humidity in the storage place of printing plates is too high

treatment method: change the plate making process; Wipe the water roller; Reset the pressure of the ink roller; Tension the blanket or repair the blanket through the tensioning device; Adjust the pH value of fountain solution or add softener and ionic agent after inspection; Change the storage conditions of printing plates

VIII. Horizontal light horizontal lines appear on the ghosting paper; The common reason is that the shadow part points are damaged

reason: the printing plate or rubber cloth is too thick; Excessive ink output; Method for grinding and cleaning the inking part of the printing plate: tighten the real fixing screw behind the oil pump with a wrench; Poor pH value of fountain solution; The ink on the layout is dry; The setting of inking roller is poor; The rubber coverage of the rubber roller is uneven

treatment method: reduce the lining thickness of printing plate or blanket; Reduce the speed of the ink supply motor or change the gap between the ink bucket and the ink bucket roller to reduce the amount of ink; Repair or replace the printing plate; Adjust the pH value of the fountain solution; Increase the speed of the water supply motor and the amount of water to prevent the ink on the layout from drying; Readjust the pressure of the inking roller; Check the parallelism of the rubber layer of the ink roller, and replace the rubber roller if necessary

IX. ink roller inking failure: the ink does not get on the ink roller, and the inking part is uneven

reason: the ink roller pressure is improper; Both ends of the rubber roller are worn or sunken, so that there is no contact mark; Ink roller cracks; The coating of inking roller and heavy roller is worn; The acidity of the fountain solution is too strong to emulsify the ink; The ink composition is wrong

the main component of this kind of film is chitosan method: if the ink cannot be evenly inked, do not use strong roller pressure to operate. The pressure of the sealing line of the roller should be uniform as a whole, and the pressure should be as small as possible within the range that does not affect the printing quality. If the rubber roller is found to be worn and dented or cracked, it should be replaced in time; If the coating of inking roller and heavy roller is worn, it should be repaired in time; Adjust the pH value of the fountain solution or replace the ink

X. irregular light dirt and whitening on the floating dirty printing surface as a whole

reason: the blanket cleaning agent flows into the fountain solution; Too much water; The viscosity of the ink is too high; Insufficient ink

treatment method: replace with clean fountain solution; Reduce the speed of water supply motor to reduce water volume; Reduce ink viscosity with reducing agent; Increase the speed of the ink supply motor and increase the ink supply

Xi. Paper feeding slack the paper feeding slack between the printer and the folding machine

reason: the tension of the web is too low; Rubber cloth lining is too thick; Paper powder accumulation on the blanket; The pressure of the paper pulling roller of the folding machine is too low; The paper cutting roller (RTF roller) and the paper pressing roller on the folding triangle are set improperly

treatment method: increase the tension of web paper by adjusting the spring or air pressure; Change the thickness of rubber cloth lining; Wipe leather cloth; Adjust the pressure of the paper pulling roller and the pressure of the paper cutting roller and the paper pressing roller until the paper is fed correctly

XII. Paper break

cause: the tension of the web or the setting of the brake are poor; Excessive fountain solution; Insufficient web tension; The parallelism of the paper guide roller is abnormal

treatment method: change the tension of the web by adjusting the relevant components to change the braking effect of the brake; Reduce water volume; Check the parallelism of the paper guide roller; Replace the web

XIII. Paper wrinkles

cause: the rubber blanket is dirty, damaged and loose, and the rubber roller is not properly lined; Excessive ink and fountain solution; The tension of the web is too large; The parallelism of the paper guide roller is abnormal or there is ink and dirt on it; Poor adjustment of folding machine; The web itself is defective

treatment method: scrub and tension the blanket, and change the thickness of its lining; Reduce ink volume and water volume; Reduce web tension; Scrub the paper guide roller and check its equality; Readjust the folding machine; Replace the web

although with the development of computers, many problems can be solved by computers, the analysis and treatment of printing faults still need operators to accumulate experience